Generally, in each of the motor drive devices that constitute a PN-busbar common system, a regenerative control device is provided to absorb the regenerative-power energy in a motor connected to each motor drive device. It is a common configuration that the regenerative-power energy is consumed by a regenerative resistor. In the following descriptions, the control designed to cause a regenerative resistor to consume the regenerative-power energy is referred to as “regenerative control”.
The regenerative control in the PN-busbar common system is required to prevent a regenerative function from being faulty due to a difference in rated regenerative power between the regenerative control devices. Therefore, it is common to operate the motor drive devices in such a manner as to enable the regenerative function of only one of the motor drive devices, which has the maximum regenerative power in the system. Therefore, there are one or more motor drive devices that have a regenerative function, although do not actually use it. Meanwhile, in the operating method as described above, the amount of power that can be regenerated is limited. Accordingly, this may not meet the maximum required regenerative power for the PN-busbar common system.
In the PN-busbar common system, it suffices that a plurality of regenerative functions that are present within the system are used in order to increase the amount of power that can be regenerated. However, in the conventional method using a plurality of regenerative functions, the PN-busbar common system is configured by only the motor drive devices having the same regenerative power, or a system that controls a regenerative load on each motor drive device is added to the PN-busbar common system, so as to operate the motor drive devices while preventing a fault in the regenerative functions. In contrast, in a case where these methods cannot be applied to the PN-busbar common system, a countermeasure is needed, such as a reduction in the load on the regenerative function by means of adding an external option dedicated to the regenerative function which has a sufficient regenerative capability, or by means of modifying the operational pattern of the motor in such a manner as to minimize the increase in bus voltage attributable to the regenerative control.
Under the technical background as described above, Patent Literature 1 listed below describes a method, in which a motor drive device having a master controller and a master function manages the regenerative capability to control the regenerative load ratio of each motor drive device within the PN-busbar common system, thereby efficiently executing the regenerative control in each motor drive device, while preventing a fault in the regenerative function due to an excess of the allowable amount of regenerative power.
Patent Literature 2 listed below describes a multiaxial motor control device. Instead of the motor drive device having a master controller and a master function, the multiaxial motor drive device executes a regenerative control in each of the motor drive devices through a network connecting the motor drive devices with each other, and therefore can prevent a fault in the regenerative function due to an overload.